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Transversely isotropic rheology in numerical models of large scale lithospheric deformation
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posted on 21.02.2017by Sharples, Wendy
Experimental and seismological studies have shown rocks with embedded faults and stratified rocks have a directionally dependent response to stress, dominated by transversely isotropic rheology. In mantle convection simulations, dynamically evolving faults and plate boundaries have, in the majority, been represented as isotropic shear bands and isotropic weak zones. Transversely isotropic constitutive models are regularly employed in the field of solid rock mechanics but have very seldom been used in the field of geodynamics. This thesis presents an exploration of transversely isotropic rheology in models of large scale lithospheric deformation. It was found that models using transversely isotropic rheology within a fault zone, produce more realistic results with regards to stress transference across the fault and displacement along the fault. The use of a transversely isotropic plasticity in time dependent models of extension resulted in more realistic lithospheric strength profiles, fault angle distributions and fault interaction. The use of a transversely isotropic plasticity in time dependent subduction zone models which include an overriding plate, facilitated asymmetric subduction from initiation to steady state subduction. In addition its use enabled the plate boundary interface to accurately evolve with time as a function of the plate boundary stresses, which led to a more accurate measurement of the stress state, dynamic topography and plate coupling in the subduction zone models. The results from all models discussed in this thesis show that a transversely isotropic rheology provides a more accurate representation of large scale deformation in the Earth's lithosphere.